1. Field of the Invention
The present invention relates to charged particle beam apparatus for use in an electron microscope, a critical dimension scanning electron microscopy (SEM), a defect detecting apparatus, charged particle beams exposure apparatus, a focused ion beam (FIB) apparatus, an Auger analysis apparatus, or the like. More particularly, it relates to a technique of reducing contaminants floating in vacuum.
2. Related Background Art
When a specimen is radiated with charged particle beams, the specimen has to be contained in a vacuum container. Because various reactant, however, exist inside the vacuum container, vacuum deterioration and beam-induced contamination is often caused.
When the specimen is placed in the vacuum container, various substances are emitted from the specimen. For example, water and hydrocarbon-based molecules is emitted from a resist coated on a wafer which is used when fine pattern is exposed to light for LSI pattern lithography. These substances are also emitted from not only the resist but also the etched wafer in some cases.
Furthermore, when the specimen is irradiated with the charged particle beams, the charged particle beams reacts with the substances on the surface of the specimen, so that the reactant are emitted into vacuum.
Additionally, there is a possibility that the substances sticking to surface of the specimen while the specimen is exposed to the atmospheric air are emitted into the vacuum container.
The substances emitted from the specimen in this manner float in the vacuum, and further possibly stick to the inner wall of the vacuum container.
Besides the reactant from the above-described specimen, in the vacuum container, there are substances such as an O ring, a vacuum grease, a resin, a wire, and the like which become sources for generating the reactant. Even when the vacuum container is left to stand in the vacuum for a long time, it is impossible to remove the hydrocarbon-based molecules included in the reactant.
As a technique for reducing the reactant which cause the vacuum deterioration and the beam-induced contamination, cooling method using a cold trap has been proposed. The cold trap cools a cooling section disposed in a place where the reactant are to be removed, and allows the cooling section to adsorb the reactant present in the vacuum. In a conventional cooling system utilizing this type of cold trap, the cooling section is cooled by supplying or circulating a cooling material such as liquid nitrogen.
However, in order to constantly keep the cooling temperature of the cooling section, the cooling material has to be constantly refilled, and so a running cost increases. Moreover, to refill the cooling material, a container such as a Dewar vessel or a bomb need to be frequently exchanged, which increases the burden of an operator. Particularly, in the case of a filling type, the temperature of the cooling section rises with the elapse of time, so that the adsorption performance of the reactant decreases by degrees during operation, and it becomes impossible to effectively reduce the reactant. Accordingly, the cooling material needs to be frequently refilled.
Moreover, the above-described conventional cooling system requires peripheral facilities such as the Dewar vessel or the bomb to be filled with the cooling material, a vacuum insulating pipe for guiding the cooling material into the apparatus, a heater for exhausting the used cooling material, and a cabinet for preventing environmental contamination due to dew condensation, so that the system is inconveniently enlarged in scale. Furthermore, when a liquefied substance is used as the cooling material, a temperature response rate of the cooling section is slow, so that it takes a long time until the temperature is stabilized.
For the above-described reasons, it has conventionally been difficult to constantly cool the cooling section and continuously use the cold trap.
The present invention has been developed in consideration of the above-described respects, and an object of the present invention is to provide charged particle beam apparatus which can efficiently remove reactant floating in vacuum, although constituted by simple structure.
To attain the above-described object, according to the present invention, there is provided charged particle beam apparatus comprising:
an optical mirror cylinder having a lens optical system for focusing charged particle beams from charged particle beam source;
a vacuum container connected to the optical mirror cylinder and containing a specimen beam on which a specimen is put;
a cooling section for adsorbing reactant present in the vacuum container;
an extremely low temperature refrigerator for cooling the cooling section;
an active damper for removing vibration generated in the extremely low temperature refrigerator; and
an active damper control section for controlling the active damper.
Moreover, according to the present invention, there is provided charged particle beam apparatus comprising:
an optical mirror cylinder having a lens optical system for focusing charged particle beams from charged particle beam source;
a vacuum container connected to the optical mirror cylinder and containing a specimen base on which a specimen is put;
a cooling section for adsorbing reactant present in the vacuum container; and
an extremely low temperature refrigerator for cooling the cooling section,
wherein the extremely low temperature refrigerator has a pulse tube for containing a gas which behaves in the same way as piston movement by using pressure vibration, and cools the cooling section by expansion of the gas in the pulse tube.
According to the present invention, the cooling section is disposed to adsorb the reactant present in the vacuum container, and the vibration generated in the extremely low temperature refrigerator is removed by the active damper, so that the deviation of the charged particle beams can be suppressed.
Moreover, the vibration amount can further be suppressed by using the extremely low temperature refrigerator of a pulse tube type.
Furthermore, by fixing the reference temperature of the cooling section in accordance with the reactant present in the vacuum container, the reactant can efficiently be adsorbed in the cooling section.
Additionally, by disposing the cooling sections on a plurality of places in the optical mirror cylinder and the vacuum container, vacuum degree can further be enhanced.